Solar energy is becoming increasingly popular in America. Although residential solar penetration rates are still quite low, solar is one of the fastest growing industries in the United States. This has caught the attention of the National Fire Protection Association—publishers of the National Electric Code—and other state and municipal regulatory authorities.
One concern raised by the rapid proliferation of solar systems is safety. During daylight hours, solar systems generate power. As a result, there is high voltage DC (potentially up to 1000 volts) or AC (potentially up to 500 volts) on the cables running from the photovoltaic (PV) array to the inverter or other power equipment located a distance away that could shock a firefighter, line worker or other maintenance personnel if they were to come in contact with those cables (e.g., to sever them) when extinguishing a fire, removing tree limbs, or performing some other operation. Therefore, it would be desirable to provide a mechanism for removing the power on the high voltage cables, e.g., via the rapid shutdown sequence. However, even in cases where rapid shutdown circuitry is used, there is no way to know with certainly, particularly in the unstable and destructive environment of a fire, tree-collapse or other disasters, what the state of the high voltage cables is. Current National Electric Code requirements do not propose any way of indicating to workers or first responders the state of a PV system even after initiating a rapid shutdown sequence.